Two-phase immersion cooling apparatus with active vapor management

ABSTRACT

A two-phase immersion cooling apparatus may include an immersion tank with a primary condenser in thermal communication with an interior volume of the immersion tank and a vapor management system fluidically connected to the immersion tank. The vapor management system may enable the apparatus to effectively manage periods of high vapor production by removing vapor and other gases from a headspace of the immersion tank, condensing the vapor to liquid, and returning the liquid to the immersion tank.

FIELD OF THE INVENTION

This disclosure relates to two-phase immersion cooling apparatuses andmethods for cooling electronic devices.

BACKGROUND

Data centers house information technology (IT) equipment for thepurposes of storing, processing, and disseminating data andapplications. IT equipment may include electronic devices, such asservers, storage systems, power distribution units, routers, switches,and firewalls.

During use, IT equipment consumes electricity and produces heat as abyproduct. A data center containing thousands of servers requires adedicated IT cooling system to manage the heat produced. The heat mustbe captured and rejected from the data center. If the heat is notremoved, ambient temperature within the data center will rise above anacceptable threshold and temperature-induced performance throttling ofelectronic devices (e.g. microprocessors) may occur.

Data centers are energy-intensive facilities. It is not uncommon for adata center to consume over 50 times more energy per square foot than atypical commercial office building. Collectively, data centers accountfor about 3% of global electricity use.

Electricity use in data centers is attributable to a variety of systems,including IT equipment, air management systems, mechanical systems,electrical systems (e.g. power conditioning systems), and coolingsystems for IT equipment. Examples of IT cooling systems includeprecision air conditioning systems, direct expansion systems, chilledwater systems, free cooling systems, humidification systems, and directliquid cooling systems. In some data centers, IT cooling and powerconditioning systems account for over half of all electricity use.

Most data centers utilize precision air conditioning systems for ITcooling. Precision air conditioners employ a vapor-compression cycle,similar to residential air conditioners. Although air conditioningtechnology is well-suited for comfort-cooling office space, it is notwell-suited for cooling thousands of relatively small, hot devicesdistributed throughout a large data center. Air has a relatively lowheat capacity, which necessitates movement and conditioning of largeamounts of air to cool IT equipment. Consequently, air conditionerssuffer from poor thermodynamic efficiency, which translates to highoperating expense. To reduce operating expense, there is a need to coolservers more efficiently.

SUMMARY OF THE INVENTION

Accordingly, advancements that improve efficiency, performance,reliability, and sustainability of IT cooling systems are needed.

In a first aspect, the invention relates to an immersion tank assembly.In some embodiments, the immersion tank assembly includes one or moreimmersion tank, each forming an interior volume, and a vapor managementsystem fluidically connected to the immersion tank assembly. In someapplications, each immersion tank may include an upper portion, a lowerportion, and a primary condenser in thermal communication with theinterior volume of the immersion tank and the vapor management systemmay include a condensing chamber forming an interior volume andincluding an inlet, an outlet, and an auxiliary condenser in thermalcommunication with the interior volume of the condensing chamber; avapor supply passage fluidically connecting the upper portion of theimmersion tank to the inlet of the condensing chamber; a valve disposedin the vapor supply passage between the upper portion of the immersiontank and the inlet of the condensing chamber; and a liquid returnpassage fluidically connecting the outlet of the condensing chamber tothe immersion tank assembly.

In some implementations, the two-phase immersion cooling apparatus mayalso include one or more of the following: a variable volume chamberfluidically connected to the vapor supply passage and disposed betweenthe upper portion of the immersion tank assembly and the inlet of thecondensing chamber; a pressure relief valve fluidically connected to thecondensing chamber; a sensor to detect pressure within the immersiontank assembly, the sensor located in the immersion tank assembly and/orin the vapor supply passage; an exhaust passage fluidically connected tothe condensing chamber; a pressure relief valve fluidically connected inthe exhaust passage; and a sensor to detect pressure within the vapormanagement system and located in the vapor management system; a waterseparator fluidically connected to the liquid return passage between theoutlet of the condensing chamber and an inlet to the immersion tankassembly; a liquid pump fluidically connected to the liquid returnpassage and disposed between the outlet of the condensing chamber and aninlet to the immersion tank assembly; a drying filter fluidicallyconnected to the liquid return passage and disposed between the outletof the condensing chamber and an inlet to the immersion tank assembly;an impurity filter fluidically connected to the liquid return passageand disposed between the outlet of the condensing chamber and an inletto the immersion tank assembly; and a vapor pump fluidically connectedto the vapor supply passage and disposed between the upper portion ofthe immersion tank and the inlet of the condensing chamber.

In a second aspect, the invention relates to an immersion tank assembly.In some embodiments, the immersion tank assembly includes one or moreimmersion tank, each forming an interior volume, and a vapor managementsystem fluidically connected to the immersion tank assembly. In someapplications, each immersion tank may include an upper portion, a lowerportion, and a primary condenser in thermal communication with theinterior volume and the vapor management system may include: acondensing chamber forming an interior volume and comprising an inlet,an outlet, and an auxiliary condenser in thermal communication with theinterior volume of the condensing chamber; a vapor supply passagefluidically connecting the upper portion of the immersion tank to theinlet of the condensing chamber; a valve disposed in the vapor supplypassage between the upper portion of the immersion tank and the inlet ofthe condensing chamber; a liquid return passage fluidically connectingthe outlet of the condensing chamber to an inlet to the immersion tankassembly; a sensor configured to detect pressure in the immersion tankassembly and to generate and transmit a signal based on a measuredpressure; and an electronic control unit configured to receive thesignal from the sensor and to send a command signal to the valve.

In some implementations, the sensor may be disposed in the immersiontank assembly and/or the vapor supply passage between the valve and theimmersion tank assembly. In some variations, the condensing chamber mayhave a volume at least 10% as large as a headspace volume of theimmersion tank. In some applications, the condenser chamber may alsoinclude a chiller fluidically connected to the auxiliary condenser. Insome embodiments, the apparatus may also include a heat exchangerfluidically connected to the primary condenser.

In a third aspect, the invention relates to a method of immersioncooling a heat-producing device. In some embodiments, the methodincludes providing a two-phase immersion cooling apparatus; detecting apressure within the immersion tank; at least one of: opening the valvewhen a measured pressure in the immersion tank assembly is greater thana predetermined threshold setting (e.g., between −0.9 psig and 0.9psig), such that dielectric vapor and other gas from the immersion tankassembly are admitted into the condensing chamber; or closing the valvewhen the measured pressure in the immersion tank assembly is less thanthe predetermined threshold setting; condensing the dielectric vapor andother gas to a liquid state in the condensing chamber; and returningcondensed dielectric liquid to the immersion tank assembly through theliquid return passage.

In some implementations, the provided immersion tank assembly mayinclude one or more immersion tank, each forming an interior volume, anda vapor management system fluidically connected to the immersion tankassembly. In some applications, each immersion tank may include an upperportion, a lower portion, and a primary condenser in thermalcommunication with the interior volume of the immersion tank and thevapor management system may include a condensing chamber forming aninterior volume and including an inlet, an outlet, and an auxiliarycondenser in thermal communication with the interior volume of thecondensing chamber; a vapor supply passage fluidically connecting theupper portion of the immersion tank to the inlet of the condensingchamber; a valve disposed in the vapor supply passage between the upperportion of the immersion tank and the inlet of the condensing chamber;and a liquid return passage fluidically connecting the outlet of thecondensing chamber to the immersion tank assembly.

In some variations, the method may also include circulating a coolantthrough the primary condenser, the coolant having a temperature greaterthan or equal to an ambient air temperature and/or circulating a firstcoolant through the primary condenser and circulating a second coolantthrough the auxiliary condenser, wherein a temperature of the firstcoolant is greater than a temperature of the second coolant.

In some implementations, the method may also include providing a vaporpump fluidically connected to the vapor supply passage and disposedbetween the immersion tank assembly and the inlet of the condensingchamber and operating the vapor pump while the valve is open to purgegas from a headspace of the immersion tank and reduce pressure withinthe immersion tank below atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a modular data center, in accordancewith some embodiments of the present invention.

FIG. 2 shows a partial cutaway view of the modular data center of FIG. 1exposing a plurality of immersion cooling tank assemblies within acontainer, in accordance with some embodiments of the present invention.

FIG. 3 shows a perspective view of an immersion cooling tank assembly,in accordance with some embodiments of the present invention.

FIG. 4 shows a perspective view of a plurality of immersion cooling tankassemblies positioned in a conventional data center, in accordance withsome embodiments of the present invention.

FIG. 5 shows a schematic diagram of a two-phase immersion coolingapparatus with a vapor management system, in accordance with someembodiments of the present invention.

FIG. 6 shows the apparatus of FIG. 5 with an open flow control valve, inaccordance with some embodiments of the present invention.

FIG. 7 shows the apparatus of FIG. 5 with an open flow control valve andexpanded bellows, in accordance with some embodiments of the presentinvention.

FIG. 8 shows a plot of immersion tank pressure and electronic devicepower consumption versus time, in accordance with some embodiments ofthe present invention.

FIG. 9 shows the apparatus of FIG. 5 with an open pressure relief valve,in accordance with some embodiments of the present invention.

FIG. 10 shows a gravity-based water separator and filtration assembly,in accordance with some embodiments of the present invention.

FIG. 11 shows an alternate embodiment of a water separator, inaccordance with some embodiments of the present invention.

FIG. 12 shows a chiller and auxiliary condenser, in accordance with someembodiments of the present invention.

FIG. 13 shows the apparatus of FIG. 5 with a vapor pump included in thevapor management system, in accordance with some embodiments of thepresent invention.

FIG. 14 shows a plot of immersion tank pressure and electronic devicepower consumption versus time when tank pressure is drawn belowatmospheric pressure prior to powering on the electronic device, inaccordance with some embodiments of the present invention.

FIG. 15 shows a prior art immersion cooling system with a primarycondenser.

FIG. 16 shows a prior art immersion cooling system with a primarycondenser and a freeboard condenser.

FIG. 17 shows an embodiment of a two-phase immersion cooling apparatuswith two immersion tanks fluidically connected to a central vapormanagement system, in accordance with some embodiments of the presentinvention.

FIG. 18 shows the apparatus of FIG. 17 with a vapor pump fluidicallyconnected between each immersion tank and the central vapor managementsystem, in accordance with some embodiments of the present invention.

FIG. 19 shows a vapor processing apparatus, in accordance with someembodiments of the present invention.

FIG. 20 shows a vapor processing apparatus with two vapor supply inlets,in accordance with some embodiments of the present invention.

FIG. 21 shows a vapor processing apparatus with a vapor pump, inaccordance with some embodiments of the present invention.

FIG. 22 shows a vapor processing apparatus with two vapor supply inletsand two vapor pumps, in accordance with some embodiments of the presentinvention.

FIG. 23 shows the apparatus of FIG. 5 with a liquid level sensorincluded in the vapor management system and a liquid pump included inthe water separator and filtration assembly, in accordance with someembodiments of the present invention.

DETAILED DESCRIPTION

Direct liquid cooling systems present a promising alternative to airconditioning systems for data center applications. One form of directliquid cooling is immersion cooling. In an immersion cooling system, anelectronic device is immersed in dielectric fluid. Waste heat from theelectronic device is transferred to the fluid and then rejected outsidethe data center. Since waste heat is not released into the ambient airof the data center, a precision air conditioning system is generally notneeded.

Immersion cooling systems may employ single-phase or two-phasetechnology. In a single-phase immersion cooling system, electronicdevices are immersed in a fluid, such as mineral oil. Waste heat fromthe electronic devices is transferred to and warms the fluid. The warmedfluid is pumped from the immersion cooling system to a heat rejectionsystem, such as an evaporative cooling tower, dry cooler, or chilledwater loop, that captures waste heat from the fluid and rejects the heatoutside the data center.

A drawback of single-phase immersion cooling technology is that mineraloil can act as a solvent and, over time, remove identifying informationfrom motherboards, processors, and other components. For instance,product labels (e.g. stickers containing serial numbers and bar codes)and other markings (e.g. screen printed information and model numbers oncapacitors and other devices) may dissolve and wash off due to acontinuous flow of mineral oil over device surfaces. As the labels andink wash off the server, the mineral oil can become contaminated and mayneed to be replaced, resulting in expense and periodic downtime. Anotherdrawback of single-phase immersion cooling is that servers cannot beserviced immediately after being withdrawn from the tank. Typically, theserver must be removed from the tank and allowed to drip dry for severalhours before servicing. During this drying period, the server may beexposed to contaminants in the circulating air, and the presence ofmineral oil on the server may attract and trap contaminants (e.g. dustor particulates) on sensitive circuitry, which may increase risk ofshort-circuiting and failure.

In a two-phase immersion cooling system, an electronic device isimmersed in a fluid, such as hydrofluoroether, in a tank. The fluidreadily evaporates and leaves no residue, so two-phase systems do notsuffer the drawbacks of single-phase mineral oil-based systems mentionedabove. During use, waste heat from the electronic device is absorbed bythe fluid, resulting in localized vaporization of the fluid. Vapor risesinto a headspace of the tank and is condensed by a condenser. Heat fromthe vapor is transferred to coolant circulating through the condenser,thereby warming the coolant. The warmed coolant is then pumped from thecondenser to a heat rejection system, such as an evaporative coolingtower, dry cooler, or chilled water loop, which captures the waste heatfrom the fluid and rejects the heat outside the data center.

Two-phase immersion cooling systems leverage the benefits of phasechange heat transfer, which makes them more efficient at and capable ofcooling electronic devices with high heat flux, such as high-performancecomputing (HPC) servers with multiple graphics processing units (GPUs),than single-phase immersion cooling systems. However, along with thebenefits of phase change heat transfer comes a challenge. In practice,retaining vapor within the system has proven challenging in prior arttwo-phase systems. Over time, existing two-phase immersion coolingsystems inevitably suffer fluid loss to the environment. The lost fluidmay be costly to replenish on a recurring basis. Examples of prior arttwo-phase cooling systems and their modes of fluid loss and othershortcomings are described below.

FIG. 15 shows a prior art example of a basic two-phase immersion coolingapparatus 1500. The apparatus 1500 includes an immersion tank 201partially filled with dielectric fluid 620 in liquid phase. Theapparatus includes a condenser 235 mounted in a headspace of the tank201. An electronic device 800 is immersed in the dielectric fluid. Theelectronic device may be a server including one or more microprocessors801. The tank 201 is enclosed by a lid 225. When powered on andfunctioning, the electronic device 800 produces heat. The heat istransferred to the dielectric fluid 620, which causes a portion of thefluid to boil and dielectric vapor 615 to form. The vapor 615 risesthrough a bath of dielectric liquid 620 and enters the headspace of thetank 201. When vapor 615 contacts the condenser 235, it condenses toliquid and passively recirculates back to the liquid bath, therebycompleting a cycle of evaporation, condensation, precipitation, andcollection. During operation, boiling of the relatively dense dielectricfluid 620 produces a relatively less dense vapor 615, which expands andenters the headspace occupied by non-condensable gases. Dielectric fluid620 occupies more volume as a vapor than liquid, so as more vapor 615 isproduced and enters the headspace, tank pressure increases. To preventthe tank pressure from reaching an unsafe level, a pressure relief valve460 is provided in the tank 201 and opened when the pressure exceeds apredetermined threshold. Upon actuation of the pressure relief valve460, dielectric vapor 615 is released from the tank 201 and lost to theenvironment. Over time, periodic valve actuation and fluid loss depletesthe fluid 620, necessitating replenishment.

In a variation of the example shown in FIG. 15, the two-phase immersioncooling apparatus 1500 can be configured to maintain a tank pressurenear ambient pressure (e.g., 1 atm) at all times. Operating at or nearatmospheric pressure may be desirable to minimize fluid losses caused byleakage or diffusion through system joints or materials, respectively.When heat load from the electronic device 800 increases, the rate ofdielectric vapor production increases and pressure builds within thetank 201. To avoid pressure accumulation, the pressure relief valve 460may be actuated whenever tank pressure rises above atmospheric pressure.During periods of intense computing, this may result in frequent ventingof vapor 615 to the environment. During idle periods, the heat load fromthe device 800 will decrease, and the rate of vapor production willdecrease or even cease. Any remaining vapor 615 is condensed by thecondenser 235 and, subsequently, air in the headspace is further cooledby the condenser 235, resulting in the tank pressure dropping belowambient pressure. To alleviate negative pressure in the tank 201, thepressure relief valve 460 may open and allow ambient air to enter thetank 201. Over time, this cyclical gas exchange results in fluid loss.

In another variation of the example shown in FIG. 15, the two-phaseimmersion cooling apparatus 1500 can be equipped with a high-capacitycondenser 235 having a cooling capacity that exceeds a maximum heat loadof the electronic device 800. The condenser 235 may operate at atemperature significantly below the vapor temperature of the dielectricfluid 620, thereby ensuring that vapor 615 is promptly condensed,thereby avoiding over-pressurization due to vapor accumulation. Althoughthis approach reduces fluid loss, the condenser 235 is large andenergy-inefficient, making it costly and impractical for large-scaledata center applications.

In another variation of the example shown in FIG. 15, the two-phaseimmersion cooling apparatus 1500 can be hermetically sealed. The tank201 can be a pressure vessel, capable of withstanding high positive ornegative pressures without risk of failure. Unfortunately, pressurevessels are costly to construct and maintain. For the sake of productliability, the effect of high-pressure operation on unique server modelswould require evaluation and approval before use, resulting in ongoingvalidation and liability burdens. High operating pressures may promotediffusion losses of fluid and accelerate aging of gaskets and othersystem components. In a sealed system, routine server maintenancerequires shutting down the cooling system and unsealing the lid toaccess to the servers, which is time-consuming. For these reasons, ahermetically-sealed tank 201 is not a practical option for most datacenters, especially those with high up-time requirements.

FIG. 16 shows a second prior art example of a two-phase immersioncooling apparatus 1600. The apparatus 1600 includes an immersion tank201 partially filled with dielectric fluid 620 in liquid phase. Anelectronic device 800 is immersed in the dielectric fluid 620. Theelectronic device 800 may be a server including one or moremicroprocessors 801. The immersion tank 201 is enclosed by a lid 225.The apparatus 1600 can include two condensers. For example, theapparatus 1600 may include a primary condenser 235 and a freeboardcondenser 250 mounted within the immersion tank 201. The primarycondenser 235 may be located above a liquid line 605 in the headspace ofthe tank 201. The freeboard condenser 250 may be located a distanceabove the primary condenser 235 in the headspace 206. In one example,the primary condenser 235 may operate at a temperature of about 5° C. to15° C. The freeboard condenser 250 may operate at a lower temperature ofabout −28° C. to −2° C. The apparatus 1600 has a high freeboard ratio,where freeboard ratio is defined as a distance measured from the top ofthe primary condenser 235 to an underside of the lid 225 divided by aninternal width of the immersion tank 201.

During steady-state operation of the apparatus 1600, vapor 615 isgenerated as heat from the electronic device 800 vaporizes fluid 620 inthe tank 201. The vapor 615 is heavier than air 705, so a first zone1605 containing saturated vapor 615 may settle above the liquid line605. A second zone 1610 containing mixed vapor 615 and air 705 may formabove the saturated vapor 615. A third zone 1615 containing mostly air705 may form above the mixture of vapor 615 and air 705. The saturatedvapor zone 1605 may be located between the liquid line 605 and theprimary condenser 235. The mixed vapor and air zone 1610 may be locatedbetween the primary condenser 235 and the freeboard condenser 250. Thethird zone 1615 containing mostly air 705 may be located between thefreeboard condenser 250 and the lid 225. The primary condenser 235 maybe appropriately sized to condense most of the vapor 615 produced duringsteady-state operation. The freeboard condenser 250 may condense vapor615 that rises above the primary condenser 235 and enters the secondzone 1610. During steady-state operation, an equilibrium of vaporproduction and condensing may exist.

During periods of high microprocessor 801 utilization, more electricpower is consumed by the device 800 and more heat is produced, resultingin a higher rate of vapor production. As the amount of vapor 615 in theheadspace 206 increases, the depth of the saturated vapor zone 1605grows. The freeboard condenser 250, which is maintained at a much lowertemperature than the primary condenser 235, may effectively condensevapor 615 that reaches it.

Although effective, the apparatus 1600 in FIG. 16 has certain drawbacks.First, the apparatus 1600 is inefficient, since the freeboard condenser250 requires a chiller to operate continuously to maintain a suitablycold temperature. Second, the apparatus 1600 is not compact oruser-friendly. To be effective, the apparatus 1600 must have a highfreeboard ratio, which necessitates a relatively tall tank 201. While atall tank 201 may be acceptable in a conventional data center with ahigh ceiling and access to a hoist or ladder to insert and removeelectronic equipment to and from the tank 201, it is not suitable for acompact application, such as an edge or mobile data center application,where the system 1600 is installed in a confined space (e.g. shippingcontainer 1005 (FIGS. 1 and 2) or utility enclosure) with heightrestrictions and minimal overhead clearance. In addition to thesepractical limitations, the cooling system 1600 in FIG. 16 may alsosuffer from fluid loss through similar modes as the cooling system 1500shown in FIG. 15 and described above.

In view of the foregoing examples, it is desirable to provide atwo-phase immersion cooling apparatus that is compact, energy-efficient,inexpensive, and experiences minimal fluid loss to the environment.

Two-Phase Immersion Cooling Apparatus with Active Vapor Management

FIG. 5 shows an embodiment of a two-phase immersion cooling apparatus100 with active vapor management in accordance with certain embodimentsof the invention. The two-phase immersion cooling apparatus 100 may beused in a variety of applications, ranging from a modular data center1000, as shown in FIG. 1, to a traditional data center 2000, as shown inFIG. 4. In the embodiment of FIG. 1, the immersion cooling apparatus 100may be positioned within a container 1005 (FIGS. 1 and 2) andfluidically connected to an external heat rejection system 240 mountedatop the container 1005.

The apparatus 100 may include an immersion tank assembly 200. Theimmersion tank assembly 200 may include an immersion tank 201 that isselectively sealable with a lid 225 (FIG. 3). The immersion tank 201 maybe vertically compact, allowing it to be placed in confined spaces, suchas shipping containers 1005 or utility enclosures associated withmodular or edge data center applications. The immersion tank 201 mayhave a height that is less than a length or width of the tank 201. Theimmersion tank 201 may have a height that is less than a length and lessthan a width of the tank 201.

The immersion tank 201 may have an upper portion 205 and a lower portion210. The upper portion 205 may be a portion of the immersion tank 201that is located above the liquid line 605. The lower portion 210 may bea portion of the immersion tank 201 that is located below the liquidline 605. The liquid line 605 may be an interface formed between gases(e.g. air and dielectric vapor) in the headspace and dielectric liquid620 in the lower portion 210 of the immersion tank 201. The immersiontank 201 may have an opening 220 in the upper portion 205. The tank 201may have an electrical insulating layer 230 on an interior surface. Theimmersion tank may have a lid 225. When open, the lid 225 may provideaccess to an interior volume 215 of the immersion tank 201 to facilitateinsertion and removal of electronic devices 800 (e.g. servers, switches,or power electronics). When closed, the lid 225 may enclose the opening220 and prevent vapor loss. The lid 225 may (e.g., hermetically-) sealthe opening 220.

The immersion tank 201 may be partially filled with (e.g., dielectric)fluid 620. The fluid 620 may be selected, or formulated by mixing two ormore fluids, to have a boiling point that is less than an operatingtemperature of a heat-generating electronic device 800, such as amicroprocessor 801. When the electronic device 800 is operating, fluid620 in contact with the device 800 may boil locally and produce vapor615. Vapor 615 may rise through the fluid bath and into the headspace206 of the immersion tank 201. The vapor 615 may settle atop the liquidline 605, forming a blanket of saturated vapor 625.

The immersion tank assembly 200 may include a primary condenser 235. Theprimary condenser 235 may be located in the headspace 206 of the tank201. The primary condenser 235 may condense vapor 615 within theimmersion tank 201. In some implementations, the primary condenser 235may be a cooling coil and, more specifically, a cooling coil thatreceives coolant, such as chilled water, water-glycol mixture,refrigerant, and the like from a heat rejection system 240, such as anevaporative cooling tower, dry cooler, or chilled water loop. The heatrejection system 240 may include a coolant pump 245, as shown in FIGS. 1and 5. The coolant pump 245 may circulate coolant through the primarycondenser 235 and heat rejection system 240.

To minimize energy consumption, the primary condenser 235 may operate ata temperature at or slightly above room temperature. In one embodiment,the primary condenser 235 may receive and circulate coolant at atemperature of about 33° C. when ambient temperature is 30° C. Inanother embodiment, the primary condenser 235 may receive and circulatecoolant at a temperature of about 25° C. to 40° C. In yet anotherembodiment, the primary condenser 235 may receive and circulate coolantat a temperature of about 30° C. to 36° C. In still another embodiment,the primary condenser 235 may receive and circulate coolant at atemperature of about 0 to 10 degrees above an ambient air temperature.In still another embodiment, the primary condenser 235 may receive andcirculate coolant at a temperature of about 0 to 15 degrees above anambient air temperature.

The apparatus 100 may include a vapor management system 400. The vapormanagement system 400 may be fluidically connected to the immersion tank201. The vapor management system 400 may receive vapor 615 from theimmersion tank 201 when necessary to avoid over-pressurization of thetank 201, condense the vapor 615 to liquid 620, and return the liquid620 to the immersion tank 201 for reuse. The vapor management system 400may be located at least partially outside the headspace 206 of theimmersion tank 201.

The vapor management system 400 may be an auxiliary vapor managementsystem, for example, an external vapor management system. The vapormanagement system 400 may activate during periods of high, variable, orsustained vapor production. The vapor management system 400 may beactivated or deactivated based on one or more system variables (e.g.tank pressure, tank temperature, or device power). The vapor managementsystem 400 may provide surplus condensing capacity to manage periods ofincreased heat load and vapor production, thereby supplementing thecondensing capacity of the primary condenser 235 when needed.

The vapor management system 400 may be actively controlled based onconditions measured or determined in the apparatus 100. For embodiment,the vapor management system 400 may be controlled based on an input ofone or more variables, such as pressure, temperature, device power,vapor concentration, or opacity within the immersion tank 201. Avariable may be measured with an electronic sensor, mechanicallydetected, estimated based on a correlated variable, or determinedthrough any other suitable technique and combinations thereof.

The vapor management system 400 may include a vapor supply passage 405.The vapor supply passage 405 may fluidically connect the vapormanagement system 400 to the upper portion 205 of the immersion tank201. The vapor supply passage 405 may be any suitable type of fluidpassage, such as, for example, a tube, pipe, integrally-formed passage,or combinations thereof.

The vapor management system 400 may include a liquid return passage 470.The liquid return passage 470 may fluidically connect the vapormanagement system 400 to the lower portion 210 of the immersion tank201. The liquid return passage 470 may be any suitable type of fluidpassage, such as a tube, pipe, or integrally-formed passage, andcombinations thereof. Together, the vapor supply passage 405 and liquidreturn passage 470 may enable circulation of fluid from and to theimmersion tank 201. For example, the vapor management system 400 mayreceive dielectric vapor 615 from the immersion tank 201 and returnliquid dielectric fluid 620 to the immersion tank 201.

The vapor management system 400 may include a valve 410 in the vaporsupply passage 405. The (e.g., flow control) valve 410 may control flowof vapor through the vapor supply passage 405. When open, the valve 410may permit vapor flow through the vapor supply passage 405 and from theimmersion tank 201 to the vapor management system 400. The valve 410 maybe a manual or automatic valve. The valve 410 may have a threshold(e.g., fixed or variable) pressure setting. In one embodiment, thethreshold pressure setting may be about 0.15 psig. In this embodiment,when pressure in the immersion tank is greater than or equal to 0.15psig, the valve 410 will open. The valve 410 may remain open until thevapor pressure in the immersion tank 201 drops below 0.15 psig, at whichtime the valve 410 may close. In another embodiment, the thresholdpressure setting may be at or between −0.15 psig and 0.15 psig. Inanother embodiment, the threshold pressure setting may be at or between−0.25 psig and 0.25 psig. In another embodiment, the threshold pressuresetting may be at or between −0.9 psig and 0.9 psig. In anotherembodiment, the threshold pressure setting may be at or between 0 psigand 0.25 psig. In another embodiment, the threshold pressure setting maybe at or between −0.25 psig and 0 psig. In another embodiment, thethreshold pressure setting may be at or between 1 psig and 5 psig. Inanother embodiment, the threshold pressure setting may be at or between4 psig and 10 psig. In another embodiment, the threshold pressuresetting may be at or between −1 psig and −5 psig. In another embodiment,the threshold pressure setting may be at or between −4 psig and −10psig.

In some embodiments, the threshold pressure setting may be variableinstead of fixed. A variable pressure setting may be useful inaddressing an anticipated surge in vapor production during transientoperation. For example, when device power consumption increases rapidly,a time lag may occur before a rise in vapor pressure is detected throughpressure monitoring. The rise in vapor production may be accuratelypredicted by monitoring device power consumption. Upon detecting anincrease in device power consumption. the threshold setting may betemporarily reduced to activate the vapor management system 400 soonerthan if a fixed threshold setting were used.

In some applications, the vapor management system 400 may include acondensing chamber 430. The condensing chamber may be a fixed volumecondensing chamber. The condensing chamber 430 may have an interiorvolume disposed between an inlet 435 and an outlet 440. The vapor supplypassage 405 may fluidically connect to the inlet 435 of the condensingchamber 430. The vapor supply passage 405 may fluidically connect anoutlet of the valve 410 to the inlet 435 of the condensing chamber 430.The vapor supply passage 405 may transport vapor 615 from the immersiontank 201 to the condensing chamber 430 when the valve 410 is open. Thecondensing chamber 430 may have a volume at least 10% as large as theheadspace volume of the immersion tank 201. The condensing chamber 430may have a volume at least 30% as large as the headspace volume of theimmersion tank 201. The condensing chamber 430 may have a volume that isat least 50% as large as the headspace volume of the immersion tank 201.The condensing chamber 430 may have a volume that is at least 70% aslarge as the headspace volume of the immersion tank 201. Headspacevolume may be a volume measured between the liquid line 605 and interiorsurface of the lid 225 and bounded by the sidewalls of the immersiontank 201.

The condensing chamber 430 may include an auxiliary condenser 451. Theauxiliary condenser 451 may be in thermal communication with thecondensing chamber 430. The auxiliary condenser 451 may extract heatfrom vapor 615 and condense the vapor 615 in the condensing chamber 430.The auxiliary condenser 451 may extend into an interior volume of thecondensing chamber 430 or be in contact with at least one surface of thecondensing chamber 430. The auxiliary condenser 451 may operate at alower temperature than the primary condenser 235. In one embodiment, theauxiliary condenser 451 may include a cooling coil connected to a liquidchiller 446. The liquid chiller 446 may circulate chilled coolantthrough the auxiliary condenser 451. In one embodiment, the liquidchiller 446 may circulate liquid at a temperature of about 5 to 15degrees C. In another embodiment, the liquid chiller 446 may circulateliquid at a temperature of about −2 to 10 degrees C. In anotherembodiment, the liquid chiller 446 may circulate liquid at a temperatureof about −10 to −5 degrees C. In another embodiment, the liquid chiller446 may circulate liquid at a temperature of about −28 to −2 degrees C.

In one variation, the liquid chiller 446 may be a refrigeration system,as shown in FIG. 12. The chiller 446 may include a pump 452 thatcirculates fluid between a reservoir 453 and a cooling coil 451 tomaintain the cooling coil at a temperature (T_(c)) that is less than theambient temperature. The fluid may be a dielectric fluid. The fluid maybe the same type of fluid used in the immersion tank 201 to reduce riskof cross-contamination from leakage or diffusion. Using the same type offluid may also simplify maintenance tasks. The liquid chiller 446 mayinclude a compressor 449, a condenser 447, an expansion valve 450, andan evaporator 448. The liquid chiller 446 may employ a refrigerationcycle to extract heat from the fluid in the reservoir 453 and rejectheat through the condenser 447.

The vapor management system 400 may include a variable volume chamber415 (e.g., a bellows). The variable volume chamber 415 may be made of avapor-resistant material, such as a metalized polyester film (e.g.,mylar), with an expandable interior volume. The variable volume chamber415 may be deflated when the pressure in the vapor management system 400is less than or equal to 1 atm. The variable volume chamber 415 mayinflate when pressure within the vapor management system 400 is greaterthan 1 atm. The variable volume chamber 415 may allow the total volumeof the vapor management system 400 to expand to increase total vaporcapacity, thereby allowing the system 400 to receive more vapor 615during transient periods. Expansion of the variable volume chamber 415may reduce pressure of incoming vapor 615 and promote condensing of thevapor 615.

The vapor management system 400 may include a pressure relief valve 460.The pressure relief valve 460 may be a safety device. The pressurerelief valve 460 may open at a predetermined pressure threshold toprevent over-pressurization of the vapor management system 400. Thepressure relief valve 460 may be fluidically connected to the condensingchamber 430 via an exhaust passage 462. In one embodiment, the pressurerelief valve 460 may be configured to open when pressure within thevapor management system 400 is equal to or greater than about 0.15 psig.In another embodiment, the pressure relief valve 460 may be configuredto open when pressure within the vapor management system 400 is equal toor greater than about 0.20 psig. In yet another embodiment, the pressurerelief valve 460 may be configured to open when pressure within thevapor management system 400 is equal to or greater than about 0.25 psig.

The vapor management system 400 may include a vapor pump 420, as shownin FIG. 13. The vapor pump 420 may be configured to purge a mixture ofair and dielectric vapor 615 from the immersion tank 201 to thecondensing chamber 430. The vapor pump 420 may be located upstream ofthe condensing chamber 430. The vapor pump 420 may have an inlet and anoutlet. The inlet of the vapor pump 420 may be fluidically connected tothe outlet of the variable volume chamber 415. The outlet of the vaporpump 420 may be fluidically connected to the inlet 435 of the condensingchamber 430. The vapor pump 420 may be capable of reducing the pressurein the immersion tank 201 below atmospheric pressure. The vapor pump 420may overcome gravitational effects on fluid flow and allow the vapormanagement system 400 to be positioned irrespective of height ororientation relative to the headspace 206, thereby providing greaterdesign freedom that may be needed when packaging the vapor managementsystem 400 in a confined space, such as a container 1005 (FIGS. 1 and 2)or utility box.

The vapor pump 420 may be useful for preemptively addressing periods ofanticipated elevated vapor production. In one embodiment, upon detectingan increase in device power consumption that will result in elevatedvapor production, the valve 410 may be opened and the vapor pump 420 maybe activated to purge vapor 615 from the headspace 206, thereby drawingdown vapor pressure within the tank 201 ahead of an anticipated pressurerise. This approach may diminish a pressure rise rate within theimmersion tank 201 resulting from increased power consumption and vaporproduction.

The vapor management system 400 may be electronically controlled. Thevapor management system 400 may include an electronic control unit 480.The electronic control unit 480 can be configured to open or close theflow control valve 410 based on a signal received from a sensor 412 orother input signal. For example, the electronic control unit 480 mayreceive an input signal (e.g., a pressure signal) from the sensor 412and, based on the input signal, send a command signal to the flowcontrol (e.g., solenoid) valve 410 to open or close. The sensor 412 canbe a pressure sensor configured to measure pressure in the immersiontank 201. The sensor 412 can be configured to transmit a signal to theelectronic control unit 480 corresponding to pressure in the immersiontank 201. The signal can be transmitted through a wired or wirelessconnection.

The electronic control unit 480 can be configured to open or close thepressure relief valve 460 based on a signal received from a sensor orother input. The sensor 463 can be a pressure sensor configured tomeasure pressure in the vapor management system 400. The sensor 463 canbe configured to transmit a signal to the electronic control unit 480corresponding to pressure in the vapor management system 400. The signalcan be transmitted through a wired or wireless connection.

The electronic control unit 480 can be configured to activate ordeactivate the vapor pump 420 (FIG. 13) based on a signal received fromthe (e.g., pressure) sensor 412. For instance, in the embodiment plottedin FIG. 14, the electronic control unit 480 may activate the vapor pump420 and purge vapor 615 from the headspace 206 to reduce tank pressurebelow atmospheric pressure prior to initiating a cooling cycle. Reducingpressure within the immersion tank 201 may reduce the boilingtemperature of the fluid 620, which may be desirable in certainapplications. In the embodiment of FIG. 14, tank pressure is drawn downbelow atmospheric pressure and the threshold pressure setting of thevalve 410 is set above atmospheric pressure, thereby allowing theoperating pressure of the tank 201 to oscillate in a range that includesvalues above and below atmospheric pressure. This method may minimizethe extent and duration of tank pressure deviations away fromatmospheric pressure, thereby minimizing fluid loss due topressure-induced diffusion or leakage. In another embodiment, tankpressure may be drawn down below atmospheric pressure and the thresholdpressure setting of the valve 410 may be set below atmospheric pressure,thereby allowing the operating pressure of the tank 201 to oscillate ina negative pressure range. This method may be desirable to reduce theboiling temperature of the fluid 620.

In some embodiments, the apparatus 100 may include a water separationand filtration system 500 (FIG. 5). As shown in FIGS. 5, 10, and 11, thewater separation and filtration system 500 may include an assembly ofone or more of the following components: a water separator 565 and afiltration system 575 that may include—for the purpose of illustrationrather than limitation—a liquid pump 585, a drying filter 590, animpurity filter 580, and the like.

For example, referring to FIG. 10, in some embodiments, the apparatus100 may include a water separator 565. The water separator 565 mayinclude an inlet 440 and an outlet 574. The water separator 565 mayreceive condensed liquid from the condensing chamber 430. The waterseparator 565 may be configured to separate water 715 or otherundesirable fluids from dielectric fluid 620. The water separator 565may capture water 715 or other undesirable fluids and allow dielectricfluid 620 to pass through. Water 715 or other undesirable fluidsaccumulated in the water separator 565 may be drained periodically. Theamount of accumulated water 715 or other undesirable fluids may dependon ambient air humidity, how well the apparatus is sealed, and howfrequently the lid 225 of the immersion tank 201 is opened.

In one embodiment, the water separator 565 may be a gravity-based waterseparator. Water 715 or other undesirable fluids may be less dense thanthe dielectric liquid 620. Consequently, captured water 715 or otherundesirable fluids may settle atop the dielectric liquid 620 within thewater separator 565. The water 715 or other undesirable fluids may bepurged from the water separator 565 periodically through a drain valve573. Dewatered dielectric liquid 620 may occupy the lower portion of thewater separator 565. Dewatered dielectric liquid 620 may be drawn fromthe water separator 565 through the outlet 574 located in the lowerportion of the water separator 565.

In an alternate embodiment, the water separator 565 may be a pump-basedwater separator. As shown in FIG. 23, the auxiliary condenser 451 mayextract heat from vapor 615 and water vapor 710 and condense the vapor615 and water vapor 710 in the condensing chamber 430. A liquid pump 576may be fluidically coupled between the condensing chamber 430 and thewater separator 565. The condensate resulted from condensing vapor 615and water vapor 710 may then be accumulated in the venting chamber,raising the liquid level in the condensing chamber 430. A liquid levelsensor 577 operatively disposed in the condensing chamber 430 may beconfigured to measure the liquid level. If the measured liquid levelexceeds a preferred liquid level, a control device may be adapted totrigger the liquid pump 576, so that all or some portion of the liquidin the condensing chamber 430 will be pumped into the water separator565. One advantage of this alternative embodiment is that with a pump576, the water separator 565 no longer needs to be placed at a locationwith sufficient gravitational potential difference with the condensingchamber 430.

In yet another embodiment, the water separator 565 may include a tiltedperforated plate 566 in a container 564, as shown in FIG. 11. Thecontainer 564 may be structured and arranged to include an inlet 571, adielectric fluid chamber 567, a dielectric fluid drain 569, a waterchamber 568, and a water drain 570. In some implementations, the waterseparator 565 may be configured to separate dielectric fluid 620 fromwater 715 based on properties of the liquids, such as differing surfacetensions. For example, HFE-7100 has a typical surface tension of 13.6dynes/cm, while water has a typical surface tension of 72 dynes/cm. As aresult, the dielectric fluid and water mixture may flow across thetilted perforated plate 566, but due to surface tension differences, thedielectric fluid 620 with a lower surface tension will flow through theperforations or holes 572 into the fluid chamber 567 beneath the tiltedperforated plate 566 while the water with higher surface tension willflow to the end of the tilted perforated plate 566 and into the waterchamber 568. While HFE-7100 is used as an example, such properties canbe exploited with any kind of dielectric fluid that has a differentkinematic viscosity than water.

The size of perforations or holes 572 in the tilted perforated plate 566may vary based on the surface tension of the dielectric fluid. Forexample, a mesh size of about 60-200 may be effective to separateHFE-7100 from water. A mesh size of 80 implies that there are 80 holesacross a square-inch area. A mesh size of 80 may include holes havingdiameters of about 0.18 mm. In another embodiment, the tilted perforatedplate 566 may be replaced with a sieve. The sieve may be made of metalwire. The sieve may have a mesh size of about 60-200.

The apparatus 100 may also include a filtration system 575. Thefiltration system 575 may include a drying filter 590 that is, in somevariations, fluidically connected to the liquid return passage 470 anddisposed between the outlet 440 of the condensing chamber 430 and theinlet of the immersion tank 201. Preferably, the drying filter 590 mayinclude a desiccant material.

The apparatus 100 may be constructed from metal, such as carbon steel.The immersion tank 201 may be constructed of metal with welded seams.Metal materials may be preferable over plastic materials, since metalmaterials may effectively prevent moisture transfer from the ambientenvironment to the dielectric fluid 620 in the tank 201. Minimizingmoisture transfer to the dielectric fluid 620 is desirable to reducedewatering demand placed on the water separator 565 and may also reducedewatering demand on the desiccant material in the drying filter 590.

In some applications, the filtration system 575 may include an impurityfilter 580. The impurity filter 580 may be fluidically connected to theliquid return passage 470 and disposed between the outlet of the dryingfilter 590 and the inlet of the immersion tank 201. The impurity filter580 may include activated carbon, charcoal, and the like. The impurityfilter 580 may capture any impurities or debris.

In some variations, the apparatus 100 may include a liquid returnsystem. The liquid return system may be configured to return dielectricliquid 620, that has been condensed from dielectric vapor, to theimmersion tank 201. The liquid return system may include a liquid pump585. The liquid pump 585 may be fluidically connected to the liquidreturn passage 470 and disposed between the outlet 574 of the waterseparator 565 and the inlet to the immersion tank 201. For example, theliquid pump 585 may be located upstream of the filters 580, 590 or,alternatively may be located downstream of the filters 580, 590.

Due to its efficient design, the two-phase immersion cooling apparatus100 may require significantly less dielectric fluid than competingdesigns that rely on relatively large internal or external reservoirs ofsubcooled fluid to function properly. Reducing fluid volume is desirableto reduce fluid cost, system weight, and system size. Minimizing sizeand weight may be particularly important in mobile applications andstationary applications where an engineered floor is not available tosupport the apparatus 100.

In some embodiments, the vapor management system 400 may only be neededperiodically. For instance, when the electronic device 800 idles,operates below its maximum power rating, operates at relatively constantpower with little variation, or the like, the vapor management system400 may not be needed until the electronic device power increases. Inother embodiments, the vapor management system 400 may be neededfrequently but may have sufficient cooling capacity to serve multipleimmersion tanks 201 simultaneously. In either scenario, a central vapormanagement system 400 may serve two or more immersion tanks 201, 201′.FIG. 17 shows an embodiment of a two-phase immersion cooling apparatus1700 having a central vapor management system 400 fluidically connectedto a first immersion tank assembly 200 and a second immersion tankassembly 200′. Employing a central vapor management system 400 may beless expensive than equipping each immersion tank 201, 201′ with aseparate vapor management system 400. Employing the central vapormanagement system 400 may conserve floor space in the data center 2000(FIG. 4). Employing the central vapor management system 400 may reduceor simplify maintenance. Each immersion tank 201, 201′ may befluidically connected to the vapor management system 400 by acorresponding vapor supply passage 405, 405′ and may be fluidicallyconnected to the water separation and filtration assembly 500 by aliquid return passage 470.

The central vapor management system 400 may monitor tank pressure ineach immersion tank 201, 201′ (e.g., using a (e.g., pressure) sensor(s)412) and receive dielectric vapor 615 from one tank 201, both tanks 201,201′, or neither tank as necessary to maintain tank pressures withinacceptable ranges. For example, the central vapor management system 400may receive vapor from the first immersion tank 201 when the firstimmersion tank pressure is at or above a first threshold pressure. Thecentral vapor management system 400 may receive vapor from the secondimmersion tank 201′ when the second immersion tank pressure is at orabove a second threshold pressure.

FIG. 18 shows a two-phase immersion cooling apparatus 1800 that variesfrom the apparatus 1700 of FIG. 17 by including a vapor pump 420, 420′that is fluidically connected between a corresponding immersion tank201, 201′ and the central vapor management system 400. Each vapor pump420, 420′ may be configured to purge a mixture of air and dielectricvapor from each immersion tank 201, 201′ and force it into thecondensing chamber 430. Each vapor pump 420, 420′ may be locatedupstream of the condensing chamber 430. Each vapor pump 420, 420′ mayhave an inlet and an outlet. The inlet of each vapor pump 420, 420′ maybe fluidically connected to the outlet of the corresponding variablevolume chamber 415, 415′. The outlet of each vapor pump 420, 420′ may befluidically connected to the inlet 435 of the condensing chamber 430.Advantageously, each vapor pump 420 may be capable of reducing thepressure in a respective immersion tank below atmospheric pressure.

In some embodiments, the vapor management system 400 may be integratedinto the two-phase immersion cooling apparatus 100 and be located in acommon enclosure. In other embodiments, the vapor management system 400may be included in a separate vapor processing apparatus 900, as shownin FIGS. 19-22, that fluidically connects to one or more immersion tankassemblies 200, 200′. The vapor processing apparatus 900 may retrofit toan existing two-phase immersion cooling apparatus 100 to boost vapormanagement capacity. For instance, if electronic devices 800 in the datacenter 2000 are upgraded and will consume more power than the electronicdevices 800 being replaced, the cooling capacity of the two-phaseimmersion cooling apparatus 100 may need to be upgraded to manage theadditional heat load. Rather than replacing the apparatus 100,alternatively, the vapor management system 400 may be added to theapparatus 100 to manage higher vapor production rates, allowing theexisting immersion tank assemblies 200, 200′ to be reused.

In some implementations, the vapor processing apparatus 900 may includean enclosure 905, as shown in FIG. 19. The vapor processing apparatus900 may include a vapor management system 400. The vapor managementsystem 400 may include a vapor supply passage 405 having a vapor supplyinlet 401. The vapor management system 400 may include a condensingchamber 430 having an inlet, an outlet, and an auxiliary condenser 451in thermal communication with an interior volume of the condensingchamber 430. The vapor supply passage 405 may fluidically connect thevapor supply inlet 401 to the inlet 435 of the condensing chamber 430.The vapor management system 400 may include a flow control valve 410 inthe vapor supply passage 405 between the vapor supply inlet 401 and theinlet 435 of the condensing chamber 430. The vapor management system 400may include a liquid return passage 470 fluidically connecting theoutlet 440 of the condensing chamber 430 to the liquid return outlet471. The vapor management system 400 may include a variable volumechamber 415 fluidically connected to the vapor supply passage 405between the vapor supply inlet 401 and the inlet 435 of the condensingchamber 430. The vapor management system 400 may also include a (e.g.,pressure) sensor 412 located in the vapor supply passage 405 andconfigured to detect pressure within an immersion tank 201, whenfluidically connected. The vapor management system 400 may furtherinclude a pressure relief valve 460 fluidically connected to thecondensing chamber 430.

The vapor processing apparatus 900 may include a water separation andfiltration assembly 500. The vapor processing apparatus 900 may include,as shown in FIG. 10, a water separator 565 and/or a filtration system575. The filtration system 575 may include one or more of: a liquid pump585, a drying filter 590, an impurity filter 580, and so forth.

FIG. 19 shows a vapor processing apparatus 900 having a single vaporsupply inlet 401. FIG. 20 shows a vapor processing apparatus 900 havingtwo vapor supply inlets 401, 401′. In other embodiments, the vaporprocessing apparatus 900 may have more than two vapor supply inlets 401,401′ to allow the apparatus 900 to receive vapor from more than twoimmersion tanks 201, 201′. In some embodiments, the vapor processingapparatus 900 may receive vapor from a grouping of immersion tanks. Forinstance, the vapor processing apparatus 900 may receive vapor from thegroupings of immersion tanks 201, 201′ disposed in plurality of tankassemblies 200, 200′, as shown in FIG. 2 or 4. Having a central vaporprocessing apparatus 900 may be more efficient and more cost-effectivethan having a vapor processing apparatus 900 for each immersion tank200.

In some variations, the vapor processing apparatus 900 may include avapor pump 420 to allow the apparatus 900 to actively purge dielectricvapor 615 and air 705 (FIG. 5) from a headspace 206 (FIG. 5) of animmersion tank 200. FIG. 21 shows a vapor processing apparatus 900 witha single vapor supply inlet 401 and a single vapor pump 420 fluidicallyconnected to the vapor management system 400. FIG. 22 shows a vaporprocessing apparatus 900 with two vapor supply inlets 401, 401′ andcorresponding vapor pumps 420, 420′ fluidically connected tocorresponding vapor supply passages 405, 405′ of the vapor managementsystem 400.

Methods of Operation

Prior to use, the immersion tank 201 may be partially filled with liquiddielectric fluid 620, as shown in FIG. 5. The remainder of the immersiontank 201 may be filled with air 705 at about atmospheric pressure (e.g.,1 atm). An interface between the liquid dielectric fluid 620 and air 705may define a liquid line 605. In some implementations, the fluid 620 maybe non-toxic. Furthermore, in some variations, the fluid 620 may benon-conductive and pose no risk to electronic devices.

Electronic devices 800 that require cooling, such as servers, switches,routers, firewalls, and the like, may be immersed in the fluid 620within the immersion tank 201, as shown in FIG. 5. For example, theelectronic devices 800 may be fully immersed and positioned below theliquid line 605. Power and communication cables (not shown) may extendfrom the electronic devices 800 to connection locations outside theimmersion tank 201. The cables may pass through an opening in the lid225 or tank wall. In another embodiment, the immersion tank 201 mayinclude integrated connectors within the tank 201 to simplify cablemanagement. In some applications, the electronic devices 800 may bearranged in a storage rack within the immersion tank 201.

Dielectric fluid 620 in the immersion tank 201 may initially be at aboutroom temperature. After the electronic device(s) 800 is immersed in thefluid and powered on, the device 800 may begin generating waste heat asa byproduct of power consumption. The heat may be absorbed by thedielectric fluid 620. If heat flux from the device 800 is sufficientlyhigh, localized boiling of the dielectric fluid 620 may occur. Boilingmay produce vapor bubbles that ascend to the liquid line 605 throughbuoyancy and enter the headspace 206 of the immersion tank 201. Thedielectric vapor 615 may be denser than air 705 and, consequently, asaturated vapor zone 625 may form atop the liquid line 605, as shown inFIG. 5. The layer of vapor may be referred to as a vapor blanket 625.When a rate of vapor production exceeds a rate of condensation, thedepth of the vapor blanket 625 will grow. Eventually, the vapor levelwill approach the primary condenser 235. Heat transfer from the vapor615 to the primary condenser 235 may promote condensing of the vapor 615to liquid 620. The condensed liquid 620 will then passively return tothe liquid bath.

When the electronic devices 800 are operating at steady-state, the rateof vapor production and rate of condensing by the primary condenser 235may reach equilibrium, resulting in a relatively constant vapor pressurewithin the immersion tank 201. Vapor pressure for HFE-7100 can becalculated using an Antoine equation shown below, where P is vaporpressure and T is temperature in degrees Celsius:ln P _(vapor)=22.415−3641.9(1/(T+273))

When power consumption by the electronic device 800 increases, wasteheat and vapor production will also increase. If elevated powerconsumption persists, at some point, the rate of vapor production mayoverwhelm the condensing capability of the primary condenser 235. Vaporpressure in the immersion tank 201 will then begin to rise. Whenpressure in the immersion tank 201 reaches a predetermined threshold,the valve 410 may open, as shown in FIG. 6, and vapor 615 will escapefrom the immersion tank 201 into the vapor management system 400. As thevapor management system 400 receives dielectric fluid vapor 615, air705, and water vapor 710 from the headspace 206 of the immersion tank201, the variable volume chamber 415 will expand, as shown in FIG. 7.

FIG. 8 shows a plot of immersion tank 201 pressure and device 800 powerconsumption versus time. In this embodiment, the electronic device 800operates at idle or low power for a period of time. During that time,vapor production may be managed entirely by the primary condenser 235,and the vapor management system 400 may remain in standby mode.Eventually, device power consumption may increase. Increased powerconsumption may produce more waste heat which, in turn, may produce moredielectric vapor 615. As vapor production increases, a condensingcapacity of the primary condenser 235 may eventually be exceeded. Asvapor 615, air 705, and water vapor 710 accumulate in the headspace 206,the immersion tank 201 pressure begins to rise until it reaches apredetermined threshold pressure setting. Upon reaching thepredetermined threshold pressure setting, as shown in FIG. 6, the flowcontrol valve 410 may be actuated (e.g., by signals from the (e.g.,pressure) sensor 412), thereby allowing vapor 615, air 705, and watervapor 710 to escape from the immersion tank 201 and enter the vapormanagement system 400. Actuation of the flow control valve 410 may causethe vapor management system 400 to switch from standby mode to activemode and the chiller 446 to turn on or reduce its setpoint temperatureto a level suitable to condense admitted vapor 615 and water vapor 710.As vapor 615, air 705, and water vapor 710 exit the immersion tank 201,the tank pressure may decrease. Eventually, the tank pressure may fallbelow the threshold pressure setting of the flow control valve 410,causing, as shown in FIG. 5, the flow control valve 410 to close andtrap vapor 615, air 705, and water vapor 710 received from the immersiontank 201 in the vapor management system 400. The vapor 615 and watervapor 710 may then be condensed within the condensing chamber 430,optionally dewatered in the water separator 565, and further dried andfiltered through the drying filter 590 and impurity filter 580,respectively, before being returned as dielectric liquid 620 to theimmersion tank 201. The vapor management system 400 may cycle on and offas needed to receive and condense vapor 615 and water vapor 710 from theimmersion tank 201 and thereby maintain pressure in the immersion tank201 at or below a desired operating pressure.

In one embodiment, it may be desirable to anticipate a rise in vaporproduction that will necessitate activation of the vapor managementsystem 400. A rise in vapor production may be anticipated by monitoringdevice power consumption. When device power consumption rises above apredetermined level or, alternately, above a predetermined level for apredetermined duration, the vapor management system 400 may switch fromstandby mode to active mode. Switching from standby mode to active modemay involve activating the chiller 446 or reducing the setpointtemperature of the chiller 446 to a level suitable to condense admittedvapor 615 and water vapor 710. This advance activation may allowsufficient time for the chiller 446 (FIG. 6) to reach a desired workingtemperature before the valve 410 is opened and vapor 615, air 705, andwater vapor 710 are admitted from the immersion tank 201. This approachallows for energy conservation when the vapor management system 400 isin standby mode, since the chiller temperature and chiller powerconsumption can be reduced.

In some instances, an unexpected heat load may be present within theimmersion tank 201 and must be safely mitigated. For example, anunexpected heat load may occur if an electronic device 800 malfunctionsand exceeds a maximum power consumption rating. If this occurs, theamount of heat and vapor 615 and water vapor 710 generated may exceedthe condensing capacity of the vapor management system 400. In practice,the flow control valve 410 will open (FIG. 6) when the tank pressurereaches the predetermined threshold setting of the flow control valve410. As vapor 615, air 705, and water vapor 710 fill the vapormanagement system 400, the bellows 415 may be configured to expand tostore additional vapor 615, air 705, and water vapor 710, as shown inFIG. 7. After the bellows 415 has fully expanded, if vapor productioncontinues to increase, pressure in the vapor management system 400(e.g., as measured by the (pressure) sensor 463) will continue to rise.To avoid mechanical failure due to over-pressurization, the pressurerelief valve 460 may be configured to actuate, as shown in FIG. 9, whenthe pressure in the vapor management system 400 exceeds a maximumallowable pressure. Vapor 615, air 705, and water vapor 710 will then bedischarged to the ambient environment, thereby reducing pressure in thevapor management system 400 and immersion tank 201 and mitigating riskof mechanical failure. Although venting vapor 615, air 705, and watervapor 710 to the ambient environment results in fluid loss, which isundesirable, fluid loss is preferable over safety risks associated withover-pressurization.

As used herein, the term “fluid” may refer to a substance in gas form,liquid form, or a two-phase mixture of gas and liquid. The fluid may becapable of undergoing a phase change from liquid to vapor or vice versa.The liquid may form a free surface that is not created by a container inwhich it resides, while the gas may not.

As used herein, the term “vapor” may refer to a substance in a gas phaseat a temperature lower than the substance's critical temperature.Therefore, the vapor may be condensed to a liquid by increasing pressurewithout reducing temperature.

As used herein, the term “two-phase mixture” may refer to a vapor phaseof a substance coexisting with a liquid phase of the substance. Whenthis occurs, a gas partial pressure may be equal to a vapor pressure ofthe liquid.

The dielectric fluid 620 may be selected for use in the immersioncooling apparatus based on a variety of factors including operatingpressure, temperature, boiling point, cost, or safety regulations thatgovern installation (e.g. such as regulations set forth in ASHRAEStandard 15 relating to permissible quantities of fluid per volume ofoccupied building space).

In some instances, fluid selection may be influenced by desireddielectric properties, desired boiling point, or compatibility withmaterials used to manufacture the immersion cooling system 100 andelectronic devices 800 to be cooled. For instance, the fluid may beselected to ensure little or no permeability through system componentsand no harmful effects to device 800 components.

A dielectric fluid 620, such as a hydrofluorocarbon (HFC) or ahydrofluoroether (HFE), can be used as the fluid in the immersioncooling apparatus 100. Unlike water, dielectric fluids can be used indirect contact with electronic devices 800, such as microprocessors 801,memory modules, power inverters, and the like, without risk of shortingelectrical connections.

Non-limiting examples of dielectric fluids include1,1,1,3,3-pentafluoropropane (known as R-245fa), hydrofluoroether (HFE),1-methoxyheptafluoropropane (known as HFE-7000),methoxy-nonafluorobutane (known as HFE-7100). Hydrofluroethers,including HFE-7000, HFE-7100, HFE-7200, HFE-7300, HFE-7500, andHFE-7600, are commercially available as NOVEC Engineered Fluids from 3MCompany headquartered in Mapleton, Minn. FC-40, FC-43, FC-72, FC-84,FC-770, FC-3283, and FC-3284 are commercially available as FLUOROINERTElectronic Liquids also from 3M Company.

NOVEC 7100 has a boiling point of 61 degrees C., a molecular weight of250 g/mol, a critical temperature of 195 degrees C., a critical pressureof 2.23 MPa, a vapor pressure of 27 kPa, a heat of vaporization of 112kJ/kg, a liquid density of 1510 kg/m³, a specific heat of 1183 J/kg-K, athermal conductivity of 0.069 W/m-K, and a dielectric strength of about40 kV for a 0.1 inch gap. NOVEC 7100 works well for certain electronicdevices 800, such as power electronic devices 800 that produce high heatloads and can operate safely at temperatures above about 80 degrees C.

NOVEC 7100 can be used to cool a microprocessor 801 that has a preferredoperating core temperature of about 60-70 degrees C. When themicroprocessor 801 is idling and has a surface temperature below 61degrees C., subcooled NOVEC 7100 near the microprocessor 801 mayexperience no local boiling. When the microprocessor 801 is fullyutilized and has a surface temperature at or above 61 degrees C., NOVEC7100 may experience vigorous local boiling and vapor production near themicroprocessor.

NOVEC 649 Engineered Fluid is available from 3M Company. It is afluoroketone fluid (C6-fluoroketone) with a low Global Warming Potential(GWP). It has a boiling point of 49 degrees C., a thermal conductivityof 0.059, a molecular weight of 316 g/mol, a critical temperature of 169degrees C., a critical pressure of 1.88 MPa, a vapor pressure of 40 kPa,a heat of vaporization of 88 kJ/kg, and a liquid density of 1600 kg/m³.

NOVEC 649 may be used to cool a microprocessor 801 that has a preferredoperating core temperature of about 60-70 degrees C. When themicroprocessor 801 is idling and has a surface temperature below 49degrees C., subcooled NOVEC 649 near the microprocessor 801 mayexperience no local boiling. When the microprocessor 801 is fullyutilized and has a surface temperature at or above 49 degrees C., NOVEC649 may experience vigorous local boiling and vapor production near themicroprocessor 801.

The elements and method steps described herein can be used in anycombination whether explicitly described or not. All combinations ofmethod steps as described herein can be performed in any order, unlessotherwise specified or clearly implied to the contrary by the context inwhich the referenced combination is made.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the content clearly dictates otherwise.

As used herein, the unit “psig” represents gauge pressure in pounds persquare inch. A positive value indicates a pressure above atmosphericpressure. A negative value indicates a pressure below atmosphericpressure.

As used herein, the term “fluidically connected” can describe a firstcomponent directly connected to a second component or a first componentindirectly connected to a second component by way of one or moreintervening components, where fluid, in gas form, liquid form, or atwo-phase mixture, may pass from the first component to the secondcomponent without escaping to the atmosphere.

Numerical ranges as used herein are intended to include every number andsubset of numbers contained within that range, whether specificallydisclosed or not. Further, these numerical ranges should be construed asproviding support for a claim directed to any number or subset ofnumbers in that range. For example, a disclosure of 1-10 should beconstrued as supporting a range of from 2 to 8, from 3 to 7, from 5 to6, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

The methods and compositions of the present invention can comprise,consist of, or consist essentially of the structural elements andprocess step limitations described herein, as well as any additional oroptional steps, components, or limitations described herein or otherwiseuseful in the art.

It is understood that the invention is not confined to the particularconstruction and arrangement of parts herein illustrated and described,but embraces such modified forms thereof as come within the scope of theclaims.

The foregoing description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the claims to the embodiments disclosed. Other modifications andvariations may be possible in view of the above teachings. Theembodiments were chosen and described to explain the principles of theinvention and its practical application to enable others skilled in theart to best utilize the invention in various embodiments and variousmodifications as are suited to the particular use contemplated. It isintended that the claims be construed to include other alternativeembodiments of the invention except insofar as limited by the prior art.

What is claimed is:
 1. A two-phase immersion cooling apparatus comprising: an immersion tank assembly comprising: at least one immersion tank, each immersion tank forming an interior volume and comprising: an upper portion; a lower portion; and a primary condenser in thermal communication with the interior volume of the immersion tank; and a vapor management system fluidically connected to the immersion tank assembly, the vapor management system comprising: a condensing chamber forming an interior volume and comprising: an inlet; an outlet; and an auxiliary condenser in thermal communication with the interior volume of the condensing chamber; a vapor supply passage fluidically connecting the upper portion of the immersion tank to the inlet of the condensing chamber; a valve disposed in the vapor supply passage between the upper portion of the immersion tank and the inlet of the condensing chamber; and a liquid return passage fluidically connecting the outlet of the condensing chamber to the immersion tank assembly.
 2. The two-phase immersion cooling apparatus of claim 1, further comprising a variable volume chamber fluidically connected to the vapor supply passage and disposed between the upper portion of the immersion tank assembly and the inlet of the condensing chamber.
 3. The two-phase immersion cooling apparatus of claim 1, further comprising a pressure relief valve fluidically connected to the condensing chamber.
 4. The two-phase immersion cooling apparatus of claim 1, further comprising a sensor to detect pressure within the immersion tank assembly, the sensor located in at least one of the immersion tank assembly or the vapor supply passage.
 5. The two-phase immersion cooling apparatus of claim 1, further comprising: an exhaust passage fluidically connected to the condensing chamber; a pressure relief valve fluidically connected in the exhaust passage; and a sensor to detect pressure within the vapor management system and located in the vapor management system.
 6. The two-phase immersion cooling apparatus of claim 1, further comprising a water separator fluidically connected to the liquid return passage between the outlet of the condensing chamber and an inlet to the immersion tank assembly.
 7. The two-phase immersion cooling apparatus of claim 1, further comprising a liquid pump fluidically connected to the liquid return passage and disposed between the outlet of the condensing chamber and an inlet to the immersion tank assembly.
 8. The two-phase immersion cooling apparatus of claim 1, further comprising a drying filter fluidically connected to the liquid return passage and disposed between the outlet of the condensing chamber and an inlet to the immersion tank assembly.
 9. The two-phase immersion cooling apparatus of claim 1, further comprising an impurity filter fluidically connected to the liquid return passage and disposed between the outlet of the condensing chamber and an inlet to the immersion tank assembly.
 10. The two-phase immersion cooling apparatus of claim 1, further comprising a vapor pump fluidically connected to the vapor supply passage and disposed between the upper portion of the immersion tank and the inlet of the condensing chamber.
 11. A two-phase immersion cooling apparatus comprising: an immersion tank assembly comprising: at least one immersion tank, each immersion tank forming an interior volume and comprising: an upper portion; a lower portion; and a primary condenser in thermal communication with the interior volume; and a vapor management system fluidically connected to the immersion tank assembly, the vapor management system comprising: a condensing chamber forming an interior volume and comprising: an inlet; an outlet, and an auxiliary condenser in thermal communication with the interior volume of the condensing chamber; a vapor supply passage fluidically connecting the upper portion of the immersion tank to the inlet of the condensing chamber; a valve disposed in the vapor supply passage between the upper portion of the immersion tank and the inlet of the condensing chamber; a liquid return passage fluidically connecting the outlet of the condensing chamber to an inlet to the immersion tank assembly; a sensor configured to detect pressure in the immersion tank assembly and to generate and transmit a signal based on a measured pressure; and an electronic control unit configured to receive the signal from the sensor and to send a command signal to the valve.
 12. The two-phase immersion cooling apparatus of claim 11, wherein the sensor is disposed in at least one of the immersion tank assembly or the vapor supply passage between the valve and the immersion tank assembly.
 13. The two-phase immersion cooling apparatus of claim 11, wherein the condensing chamber has a volume at least 10% as large as a headspace volume of the immersion tank.
 14. The two-phase immersion cooling apparatus of claim 11, wherein the condenser chamber further comprises a chiller fluidically connected to the auxiliary condenser.
 15. The two-phase immersion cooling apparatus of claim 11, further comprising a heat exchanger fluidically connected to the primary condenser.
 16. A method of immersion cooling a heat-producing device, the method comprising: providing a two-phase immersion cooling apparatus comprising: an immersion tank assembly comprising: at least one immersion tank, each immersion tank forming an interior volume and comprising: an upper portion; a lower portion; and a primary condenser in thermal communication with the interior volume of the immersion tank; and a vapor management system fluidically connected to the immersion tank assembly, the vapor management system comprising: a condensing chamber forming an interior volume and comprising:  an inlet;  an outlet; and  an auxiliary condenser in thermal communication with the interior volume of the condensing chamber; a vapor supply passage fluidically connecting the upper portion of the immersion tank to the inlet of the condensing chamber; a valve disposed in the vapor supply passage between the upper portion of the immersion tank and the inlet of the condensing chamber; and a liquid return passage fluidically connecting the outlet of the condensing chamber to the immersion tank assembly; detecting a pressure within the immersion tank; at least one of: opening the valve when a measured pressure in the immersion tank assembly is greater than a predetermined threshold setting, such that dielectric vapor and other gas from the immersion tank assembly are admitted into the condensing chamber; or closing the valve when the measured pressure in the immersion tank assembly is less than the predetermined threshold setting; condensing the dielectric vapor and other gas to a liquid state in the condensing chamber; and returning condensed dielectric liquid to the immersion tank assembly through the liquid return passage.
 17. The method of claim 16, further comprising circulating a coolant through the primary condenser, the coolant having a temperature greater than or equal to an ambient air temperature.
 18. The method of claim 16, further comprising: circulating a first coolant through the primary condenser; and circulating a second coolant through the auxiliary condenser, wherein a temperature of the first coolant is greater than a temperature of the second coolant.
 19. The method of claim 16, further comprising: providing a vapor pump fluidically connected to the vapor supply passage and disposed between the immersion tank assembly and the inlet of the condensing chamber; and operating the vapor pump while the valve is open to purge gas from a headspace of the immersion tank and reduce pressure within the immersion tank below atmospheric pressure.
 20. The method of claim 16, wherein the predetermined threshold setting is between −0.9 psig and 0.9 psig. 